Question

i) if 18p r-1 :17pr-1
= 9:7, find r.​

Answer 1

Answer:

As we know that,

nPr=(n−r)!n!

Therefore,

18Pr−1=(18−(r−1))!18!=(19−r)!18!

17Pr−1=(17−(r−1))!17!=(18−r)!17!

Now,

17Pr−118Pr−1=79

((18−r)!17!)((19−r)!18!)=79

((18−r)!